1. Field of the Invention
The present invention is related to etching of chrome from calcium fluoride (CaF2) objects.
2. Background Art
Typically, chrome is deposited and etched on a surface of CaF2 material to form a pattern on the surface of the CaF2 material. For example, one manufacturer of CaF2 material is SCHOTT Lithotec AG of Germany. Etching chrome from a high quality, low micro-roughness finish CaF2 material can damage the surface beyond a threshold amount. This is because the CaF2 material cannot be reworked or repolished because such subsequent processing would further damage or destroy the patterned surface. Thus, a threshold amount of damage is established that allows light to transmit through the CaF2 material with only a predetermined amount of absorption and/or scattering of the light.
In one example, the CaF2 material can be used as an optical element in 157 nanometer (nm) lithography tools. However, if a level of damage is severe enough (e.g., greater than a few Angstroms deep) the optical element cannot be used because it most likely will not properly transmit light at this wavelength (e.g., too much light will be absorbed and/or scattered).
Therefore, what is needed is a method of etching chrome from a surface of CaF2 material, while maintaining a micro-finish on surface of the CaF2 material.